How to share a LAN Internet Connection over Bluetooth PAN//Ad-Hoc WiFi?

[mikeyquema]

I use a Windows XP Laptop with a LAN connection here at the office. My xp office laptop is connected to the office file server as well as the internet behind the office firewall which requires me to log in via IE so i can access the internet. My personal laptop is a MacBook running OS X and i would like to share the internet connection form my office laptop either over Bluetooth or WiFi.
I know it would be easier to do this from OS X but i need it to be from my xp laptop.
The digram would be:
Internet<=>LAN<=>XP<=>WiFi or Bluetooth<=>Mac OS X
My office laptop acting as a virtual internet router.

Thanks in advance!